1. Field of the Invention
The present invention relates to a technique of bonding a lamp body and a lamp lens to each other to form a vehicular lamp, and more particularly to a bonding structure and a bonding method in which an adhesive agent is solidified by a so-called "dielectric heating method" in which a high frequency voltage is applied to a dielectric bonding agent applied to the seal groove of a lamp body, thereby to fixedly bond the leg of the lens to the seal groove of the lamp body.
2. Related Art
FIGS. 10 and 11 show a conventional structure of a vehicular lamp. According to the conventional structure, a front opening of a lamp body 50 formed from polypropylene resin (hereinafter referred to as "PP resin", when applicable) or the like is covered with a front lens 51 (hereinafter referred to merely as "a lens 51", when applicable) made of glass, PC resin, PMMA resin, or the like, and a small lamp bulb 53 is fitted at the focal position F of a reflector 52 formed on an inner surface of the lamp body 50. The lens 51 is fixedly bonded to the lamp body 50 as follows: First, the seal groove 54 of the lamp body 50 (hereinafter also referred to as a joint part of the lamp body) is filled with a hot melt sealing agent 55, and then the leg 56 of the lens 51 (hereinafter also referred to as a joint part of the lens) is fitted in the seal groove 54 of the lamp body 50. In addition, mechanical tightening means 57 such as a plate spring, a lance, and screws is employed to combine the lens with the lamp body.
In the conventional above-described bonding method, the molten hot melt sealing agent 55 is applied to the seal groove 54 and the leg 56 which are the joint parts of the lens and the lamp body, and thereafter the agent 55 thus applied is cooled. The bonding of the leg 56 to the seal groove 54 is accomplished within several minutes. Hence, the method is advantageous in that it is high in productivity, so that the vehicular lamp requires low manufacturing cost. However, the method suffers from a difficulty that, since the hot melt sealing agent 55 is thermoplastic material, the resultant vehicular lamp is low in heat resistance. Hence, in order to increase the force of adhesion between the joint parts 54 and 56, it is necessary to utilize the above-described mechanical tightening means 57. Furthermore, in order to improve the water resistance of the joint parts 54 and 56, it is necessary to increase the widths (x and y) of the seal groove 54, thereby to increase the quantity of hot melt sealing agent 55 applied to the seal groove 54. However, this may make the external appearance of the joint parts 54 and 56 vehicular lamp unattractive.
On the other hand, the thermoplastic adhesive agent is not well bonded to the PP resin. In order to solidify it, a heat solidifying method using hot air or infrared rays, or a wet solidifying method is employed. Therefore, the method is low in productivity. Furthermore, with the method, resin members such as the lamp body and the lens may be deformed. Hence, the method is not applicable to the manufacture of vehicular lamps.